1. Field of the Invention
The present invention relates to a height measuring apparatus and method for measuring heights of an object for imaging such as electronic components as well as to a testing apparatus for testing an object and measuring its heights by using such a height measuring apparatus.
2. Description of the Prior Art
Conventionally, after electronic components have been mounted on a mounting circuit board, the mounting of the electronic components is tested visually according to the following method.
For example, as for a mounting circuit board 1, each electronic component to be tested is imaged by an imaging section 3 by using a lens 2 having a relatively high magnification as shown in FIG. 9A and is visually tested while an operator looking at an imaged picture taken by the imaging section 3 (see FIG. 9B).
In this case, since individual electronic components have different surface heights, the heights of the respective electronic components are detected by imaging the electronic components by using a separately provided measuring instrument such as a laser measuring instrument or by utilizing what is called an overall focusing method.
The overall focusing method is a method for obtaining an imaged picture that is in focus in the entire range by imaging the electronic components with the imaging section 3 while moving an imaging means, that is, the lens 2 and the imaging section 3, in the height direction with respect to the electronic components with a moving means by a very small distance at a time and then synthesizing a picture by picking up portions including in-focus components of imaged pictures at the respective heights.
This method allows recognition of the heights of the respective components based on the movement distances of the imaging section 3 that is moved by the moving means.
However, in recent years, the integration density of electronic components etc. has increased and a video camera has come to be used to test minute components visually.
As shown in FIGS. 10A and 10B, in the case of using a video camera 4 a lens 5 having a relatively small magnification and a large depth of field is used because a wide region of a mounting circuit board 1 needs to be tested. Therefore, in appearance a wide area is in focus and hence the above-mentioned overall focusing method cannot be utilized.
Therefore, the heights of the respective components cannot be measured simultaneously with testing. To measure the heights of the respective components, a separately provided height measuring instrument is needed. This causes a problem of increase in equipment cost.